The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Truck, bus and other heavy duty applications are commonly designed using an independent front and/or an independent rear suspension system to connect the chassis of the vehicle (the unsprung portion) and the body of the vehicle (the sprung portion). The independent suspension systems normally include an upper control arm, a lower control arm and a hub or knuckle which supports the tire of the vehicle. Each control arm is attached to the frame or other structural component of the vehicle using one or more elastomeric bushings. Each elastomeric bushing usually consists of an outer metal tube which is pressed into the control arm, a layer of elastomer positioned within the outer metal housing and an inner metal housing which extends through the center of the layer of elastomer. The inner metal housing is attached to a bracket on the frame, the supporting structure or the sprung portion of the vehicle or a bolt extends through the inner metal and secures the end of the control arm to the frame, the supporting structure or the sprung portion of the vehicle by mating with an appropriate bracket. As the vehicle travels, relative movement between the sprung and unsprung portions of the vehicle is accommodated by flexing of a coil spring, a torsion bar, an air spring or by another resilient device. The flexing of the resilient device causes the ends of the control arms to pivot on both of the pivot bushings which secure the control arms to the sprung portion of the vehicle.
The elastomeric bushings are used to facilitate this pivotal motion and to isolate the vehicle from shock. The layer of elastomer located between the inner and outer metal housings effectively isolates the sprung portion of the vehicle from the unsprung portion of the vehicle. In certain high load applications, the ends of the outer metal are curved or formed over towards the inner metal in order to further encapsulate the layer of elastomer. The curving or forming of the ends and thus the further encapsulating of the layer of elastomer improves the radial spring rate, it improves the axial spring rate, it improves the axial retention and it improves the durability of the bushing.
While these elastomer isolated pivot bushings have performed satisfactorily in the field, they are not without their problems. The various problems associated with these prior art pivot bushings include variations in the diameters of the control arms and distortion of the cross section in the area where the pivot bushing is pressed into the control arms. These manufacturing variations in the configuration of the control arms, often allow the bushing to slip out of the control arm when the control arm undergoes an axial load.
Also, in the higher load and the higher travel applications, the rotational angles that the pivot bushing must travel through places a detrimental effect on the life of the elastomeric component of the pivot bushing.
Thus, the continued development of pivot bushings has been directed to the improvements of rotational capabilities, the improvements of performance, the improvements of strength and the improvements of durability while minimizing the manufacturing costs associated with the pivot bushing.